The present invention relates to the field of power systems. In particular, the present invention relates to an elevator power system including a regenerative drive operable to provide automatic rescue operation and to charge the backup power source associated with the automatic rescue operation.
An elevator drive system is typically designed to operate over a specific input voltage range from a power source. The components of the drive have voltage and current ratings that allow the drive to continuously operate while the power supply remains within the designed input voltage range. However, in certain markets the utility network is less reliable, and utility voltage sags, brownout conditions (i.e., voltage conditions below the tolerance band of the drive) and/or power loss conditions are prevalent. When utility voltage sags occur, the drive draws more current from the power supply to maintain uniform power to the hoist motor. In conventional systems, when excess current is being drawn from the power supply, the drive will shut down to avoid damaging the components of the drive.
When a power sag or power loss occurs, the elevator may become stalled between floors in the elevator hoistway until the power supply returns to the nominal operating voltage range. In conventional systems, passengers in the elevator may be trapped until a maintenance worker is able to release a brake for controlling cab movement upwardly or downwardly to allow the elevator to move to the closest floor. More recently, elevator systems employing automatic rescue operation have been introduced. These elevator systems include electrical energy storage devices that are controlled after power failure to provide power to move the elevator to the next floor for passenger disembarkation. However, many current automatic rescue operation systems are complex and expensive to implement, and may provide unreliable power to the elevator drive after a power failure. In addition, current systems require a dedicated charger for the backup power source associated with the automatic rescue operation procedure.